A sheet cutting device of this type includes a fixed blade unit including a fixed blade and biasing means for pressurizing the fixed blade against a movable blade, and a movable blade unit including the movable blade and drive means that is connected to a drive source and drives the movable blade in a stroke direction. The fixed blade and the movable blade are opposed to each other across front and back surfaces of a sheet that has undergone printing in a sheet passage inside a printer.
The sheet cutting device including the fixed blade and the movable blade is disclosed in, for example, Related Art Document 1 of this invention (Japanese Unexamined Patent Application Publication (JP-A) 2001-347485).
Referring, as an example of the sheet cutting device, to FIGS. 1A to 1C illustrating only the fixed blade and the movable blade included in the fixed blade unit and the movable blade unit, respectively, a movable blade 72 includes a blade edge portion 72a that engages with a blade edge portion of a fixed blade 12, and a pair of guide portions 72c that protrudes toward an engagement starting end side (in the figures, upper side) with respect to the blade edge portion 72a at both ends of the movable blade 72 in its width direction, which corresponds to a width direction of a sheet S, the pair of guide portions 72c being configured to guide the engagement with the fixed blade 12 at the time of cutting. Note that, the pair of guide portions 72c is bent as illustrated in FIG. 1B.
This sheet cutting device operates as follows. The sheet S conveyed from the right to left of FIG. 1A is temporarily stopped, and the drive means causes the movable blade 72 to move (ascend) in a stroke direction K. The fixed blade 12 and the movable blade 72 are provided in a press-contact (engagement) state to each other by the biasing means, and hence the sheet S is cut by the principle of scissors. The cut sheet is delivered from a delivery port of the printer.
Generally, the movable blade has its outer shape formed by punching a metal plate material with use of dies.
After the punching of the outer shape, bending is carried out to form the pair of guide portions into a shape which is curved so as to increase its distance from the fixed blade as approaching the leading end (end at which engagement with the fixed blade starts) as illustrated in FIG. 1B.
At the time of punching, a movable die (not shown) is punched into the metal plate material in a direction indicated by an arrow P in FIG. 1C. In FIG. 1C, reference symbol Pf represents a punching front side, and reference symbol Pr represents a punching rear side.
By the way, after the punching of the metal plate material, as illustrated in FIG. 1C, an outer edge portion on the punching front side Pf has a shape called a shear droop, while an outer edge portion on the punching rear side Pr has a shape called a burr. Note that, in the accompanying drawings including FIG. 1C of this specification, for the sake of easy understanding of the description, the sizes and shapes of the shear droop and the burr are illustrated in an exaggerated manner.
The blade edge portion of the movable blade is required to engage with the blade edge portion of the fixed blade, and hence an outer edge portion without the shear droop, that is, the outer edge portion on the punching rear side is used therefor.
As described above, in the movable blade which has its outer shape formed by punching, burrs are generated on the outer edge portion on the punching rear side. Those burrs are also generated on the outer edge portion of each of the pair of guide portions on the punching rear side. Therefore, along with the engagement of the movable blade with respect to the fixed blade, the burr on the outer edge portion of each of the pair of guide portions on the punching rear side, in particular, the burr of the movable blade, which extends in the stroke direction, slides on the surface of the fixed blade. Even when the movable blade 72 is engaged with the fixed blade 12 without problems in the beginning as illustrated in FIGS. 2A and 2B, along with the elapse of operating time of the sheet cutting device, abrasion of the fixed blade 12 due to the burr of the pair of guide portions 72c progresses. As a result, as illustrated in FIGS. 2C and 2D, the burr of the pair of guide portions 72c digs into the original surface of the fixed blade 12, and accordingly the movable blade 72 is shifted on the fixed blade 12 side. In this case, there is a fear that the blade edge portion 72a of the movable blade 72 may hit the fixed blade 12 to cause locking and damaging, which may lead to problems such as losing the ability to cut the sheet.